OBJECTIVES: The major objectives of this study are to determine the effectiveness of a zinc sulfate nutritional supplement as a preventive or cure for recurrent idiopathic oral ulcers (recurrent aphthous ulcers) and to evaluate the levels of folic acid and vitamin B12 with respect to the occurrence of these ulcers. A further objective is to evaluate in these patients the levels of some other trace metals including cadmium, manganese, copper and chromium which may compete metabolically with zinc. METHODS: Diagnosis of the idiopathic oral ulcers will be made on the basis of history, clinical examination and other necessary confirmatory means such as cytology, biopsy or culture. Other similar types of ulcers or lesions will be ruled out by serology, complete blood counts or chemistries as necessary. Plasma zinc, iron, copper, cadmium, manganese and chromium determinations will be done as well as serum or RBC folic acid and serum vitamin B12. Patients will be provided zinc sulfate and placebo supplementation on a double blind basis. The trace metals and vitamin levels being studied will be monitored regularly for changes. Duration, frequency, numbers and size of the ulcers which occur will be observed. Patients found to have folate or vitamin B12 deficiencies will be treated appropriately for these in addition to the zinc or placebo supplementation.